The present invention concerns a method for the treatment of residues produced by the incineration of urban and industrial wastes, and the products obtained by such a method.
The problems raised by the increasing production of wastes of all types, both by industries and by urbanized areas, are growing in number and in difficulty. Moreover, growing environmental concerns have given rise to laws having strict standards, making it increasingly difficult to dispose of these wastes by direct dumping, by storage, or by underground introduction or burial.
In the future, it must be therefore expected that techniques such as incineration will play a vital role, by offering acceptable means to destroy these wastes in terms of environmental pollution. By employing thermal decomposition by thermal oxidation at high temperature to decompose the organic fractions of the wastes and reduce the volumes, the incineration sometimes also generates its own wastes. The different types of waste incineration residue can be classified into two main categories: slags, which can be upgraded, and flue gas treatment residues. The latter include fly ash and soot taken from a simple dust collector, residues from filter-presses, and dechlorination residues. When the wastes are burned in an incinerator, several types of waste are generated, depending on the waste treatment method. Four methods can be employed for treating flue gas treatment residues: dry and semi-dry method, and semi-wet and wet methods.
In the dry method, a dry, powdery reactant is pneumatically injected. The solid absorbs the pollutants, which are neutralized by dry reaction and at high temperature (200.degree. to 300.degree. C.), and the reaction products and excess reactant must then be collected.
In the semi-dry method, to improve the collection efficiency, the dry reactant is injected into the flue gases that are previously humidified and cooled to 140.degree. to 190 .degree. C. in a specific reactor.
In the semi-wet method, a sludge reactant is injected into the flue gases, and a filter system collects the reaction products and excess reactant.
The wet method takes places in three phases:
upstream dust collecting designed to remove the largest dust particles, PA1 gas scrubbing, PA1 treatment of the wash waters. PA1 a first step of chemical analysis of the urban or industrial waste incineration residues in order to determine: PA1 a second step in which the urban or industrial waste incineration residues are mixed or crushed, with said hydraulic binder and additives, followed by granulation with water of the mixture obtained, with the granules then left to harden, the nature and proportion of said hydraulic binder and said additives having been selected in order to allow both the physical and/or chemical neutralization of the harmful elements for setting or hardening of said hydraulic binder present in the wastes, as well as the production of granules with low porosity and low permeability. PA1 the overall action of the soluble ions which are detrimental to the setting or hardening of a Portland cement released during the soaking of the waste in water, PA1 and the soluble sulfate content. PA1 samples of the incineration residue are taken and soaked in water, allowing for a ratio of the mass of water to the mass of residue of about 10, PA1 the aqueous solution is analyzed in a known manner, for example by X-ray fluorescence, or by the method known as the inductively coupled plasma (ICP) method. PA1 SiO.sub.2 from 15 to 45%, Al.sub.2 O.sub.3 from 9 to 26%, Fe.sub.2 O.sub.3 from 0.5 to 10%, CaO from 9 to 53%, MgO from 1 to 7%, Na.sub.2 O from 0.5% to 6%, K.sub.2 O from 0.3 to 6%, sulfates from 2 to 10%, and Cl from 0.5 to 6% PA1 Zn from 40 to 70%, Pb from 1 to 30%, Cu from 0 to 5%, Sn from 1 to 5%, Ba from 0.5 to 9.52%, Cd from 0.5 to 2%, total Cr from 0.5 to 2%, Ni from 0.2 to 1%, Cd from 0.1 to 1%, Ag from 0.2 to 1%, Hg from 0.01 to 0.05%, As from 0.24 to 0.4%, Mn from 0.5 to 6%, Ti from 5 to 20%, Se from 0.01 to 0.10%, Be from 0.01 to 0.1%, V from 0.1 to 1% and F from 0.01 to 0.20% PA1 the proportions of hydraulic binder are expressed as mass percentages of hydraulic binder (additive included) related to the mass of mixture of residue+binder, PA1 the proportions of additive are expressed as mass percentages of additive related to the mass of hydraulic binder and additive, PA1 the proportions of water are expressed as mass percentages of water related to the mass of hydraulic binder and additive.
Waste incineration residues fall into the category of wastes covered by laws enacted to limit air, water and soil pollution, creating a constant need for more efficient systems to make them inert for subsequent disposal in a technical burial center or recycle. Many workers have attempted to develop such systems.
According to a first alternative, it was proposed to mix these wastes with a hydraulic binder with a view to subsequent dumping.
Thus U.S. Pat. No. 4,744,829 describes a method for the production of leach-resistant agglomerates from wastes such as ash and filter dusts, according to which the wastes are finely ground and then introduced into a colloidal suspension of cement. The granules produced from this mixture are hardened to withstand leaching.
The main drawback of such a method resides in the fact that the number of interactions between the waste and the cement is considerably increased by enlarging the contact surface area between the waste and the cement due to intense crushing of the wastes. This means that the anticipated result is only reached if the waste contains virtually no elements that are liable to disturb the setting of the cement. Furthermore, obtaining a colloidal suspension of cement implies the use of a cement that has undergone prior supercrushing and has a high water/cement (W/C) ratio of about 2. In these conditions, the structure of the granules obtained is too porous to withstand leaching successfully.
This first alternative is also described in U.S. Pat. No. 3,947,293, which recommends conditioning the waste incineration residues with Portland cement and lime or Portland cement and calcium sulfoaluminate or sulfate compounds.
In fact, the waste incineration residues may contain elements and compounds which interact with the hydraulic binders, disturbing the setting and hardening processes (delay or acceleration of setting leading to rapid stiffening and consequently a brittle fragile product), or may cause swelling (expansion). Stabilization by hydraulic binders is hence incomplete and ineffective because subsequent leaching is favored by the cracks and/or breaks formed during setting and hardening and also subsequently.
With respect to household residues, the problems that arise are connected with heavy metals such as Hg, Cd, Zn, Cu, Ni and Cr, and with chlorine, sulfate and cyanide ions originating in the main residues: organic matter and plastics, paper and cardboard, textiles, leather and rubber, glasses, metals and batteries.
Each of these ions or metals can cause delays or accelerations in setting and swelling, and these problems tend to deteriorate the cement paste and prevent it from playing its role as a hydraulic binder.
To overcome these drawbacks, a second alternative has been recommended, consisting of adding one or more of the following products to the waste incineration residues, if necessary in a mixture with an additional hydraulic binder: bentonite (U.S. Pat. No. 4,149,968), vermiculite (U.S. Pat. No. 4,113,504), rice husks (Japanese Patent No. 77.110.744), sodium or calcium lignosulfonates (Japanese Patents No. 81.53.796 ) and No. 75.44.977), calcium aluminate (Japanese Patent No. 75.93.264), polyvinyl acetate, aluminum stearate (Japanese Patent No. 79.162.844), sodium bicarbonate (Japanese Patent No. 80.44.355), polymers (Japanese Patent No. 80.29.119 and U.S. Pat. No. 4,174,293), polyvinyl alcohol (Japanese Patent No. 77.111.260), slag and gypsum (U.S. Pat. No. 4,266,980), calcium sulfate (U.S. Pat. No. 3,947,284), calcium chloride (U.S. Pat. No. 1,909,849), water-soluble silicates (U.S. Pat. No. 2,081,541, No. 3,837,872, No. 3,841,102, No. 4,012,320, No. 3,892,636, No. 4,600,514 and No. 4,518,508), systems based on lime and fly ash, lime and clay, or lime and cement kiln dusts (U.S. Pat. No. 3,720,609).
However, the problems of setting and hardening of the hydraulic binder, mentioned above, subsist because the waste incineration residues are not chemically inert, and interact with the binder. In fact, the wastes carry along with them their content of ions or heavy metals, which disturb the setting and hardening phenomenons, and give rise to swelling and expansion which causes subsequent fracture or cracking of the material. The leach resistance is considerably decreased. Such problems tend to render ineffective the stabilization of waste incineration residues by hydraulic binders according to the above systems.
In a third alternative, it was proposed to condition the waste incineration residues in at least two stabilization steps: a first step in which the residues are mixed with a hydraulic binder and possibly various reagents to trap the environment-unfriendly elements chemically or physically, followed by a second step, designed to reinforce the action of the hydraulic binder used in the first step, which consists of providing a barrier to prevent leaching phenomenons. Depending on each specific case, the barrier may be obtained by coating using a composition based on a hydraulic binder such as water and cement, or an organic binder such as a stearate or bitumen. Many special systems have been proposed, describing the two-step conditioning of waste incineration residues. One such solution has been described in particular in Japanese Patent Application No. 61.0910050, in International Application No. 89/12498, and in German Patent No. 3.808.187.
Japanese Patent Application No. 61.09 10050 concerns a method for the fabrication of aggregates or fillers for concrete, using incineration ash. By this method, the ash is crushed, mixed with cement (about 40% by weight) and treated until the cement is partly or completely hardened. The concrete thus obtained is then reduced by crushing to particles, which are again mixed with cement (about 40% by weight) and possibly sand. After hardening, another reaction is carried out by crushing to obtain particles of predetermined size or aggregates, which are then used to make concrete.
This solution is however uneconomic because it comprises several crushing steps and requires large quantities of cement. It tends to solve the problems of setting and hardening mentioned above, by diluting the wastes in cement. Due to the crushing operations, interactions with the hydraulic binder and harmful elements for setting and hardening of the binder are favored, both in the first step and in the second. This is why it is not possible to achieve effective stabilization of all the wastes in a dense structure, and if these harmful elements are present.
According to International Application No. 89/12498, the waste incineration residues are combined with a treatment agent for heavy metals such as diatomaceous clay, to which Portland cement is preferably added, and the granulates obtained are then coated with a cement composition.
Even in this case, however, the harmful elements for setting and hardening present in the residues, such as Cl--.sub.4, SO.sub.4 --ions, . . . can hinder the hydration of the cement used to form the granulates, and consequently the cement making up the coating shell, at least at the periphery of the shell in contact with the granulate. This leads to an absence of a physical or chemical bond between the granulate and the coating shell, causing embrittlement of the latter, which could accordingly break in the case of impact, deformation or strong expansion.
The solution proposed by German Patent No. 3.808.187 consists of crushing the wastes, subjecting them to treatment with lime, followed by granulation under pressure, heat treatment and crushing. The mixture obtained is then mixed with cement, and again granulated.
These solutions leave the problems mentioned above unresolved, or require even more cumbersome treatments to attempt to solve them.
The methods described in the prior art hence do not take account of the variety of the residue compositions and are hence only feasible with restricted ranges of products to be treated.
This means that, so far, no method for the treatment of waste incineration residues has yet been proposed that is simple, applicable to all incineration wastes, and also effective in so far as it guarantees effective stabilization in terms of environmental pollution, in the short, medium and long term. The present invention is therefore aimed to remedy the drawbacks mentioned above and to propose such a treatment method.